Page.FindControl comes back null for DIV

Question

I have a page where I create div controls dynamiclly and number them automaticlly.

subCell = new TableCell();
subCell.Controls.Add(new LiteralControl(
    "<div id=\"picker" + Index.ToString() + "\" runat=\"server\" 
     class=\"colorSelector\"><div style=\"background-color: #000000;\">Text
     </div></div>"));
subRow.Cells.Add(subCell);
subTb.Rows.Add(subRow);

Later in the code I want to get the background-color value like so:

HtmlGenericControl div;

div = (HtmlGenericControl)Page.FindControl("picker" + e.CommandArgument.ToString());

string colorCode = div.Style["background-color"].ToString();

after these line of code I get a null object ref error. div is null. I have tried HtmlControl and LiteralControl as the object type and that does not help either.

Thank you!

Jason Goemaat · Accepted Answer · 2011-06-01T07:54:17.390

Page.FindControl only works for server controls. You are assigning an id to text within the literal control which happens to be a div, but not the control itself. If you set the id of the control you should be able to find it, but I don't know if that's what you're intending.

In response to your comment, check your HTML. The runat=server will probably be there because ASP.NET isn't processing it as a control, it is treating it as content. Try something like this, noting that Page.FindControl only works on immediate children. Here I've declared a server panel named 'declaredPanel' in the aspx. ClientIdMode.Static makes it so ASP.NET won't add parent names to the control (like "MainContent_childPanel")

<asp:Panel ID="declaredPanel" runat="server" ClientIDMode="Static" />

In Page_Load:

    Panel p = new Panel();
    p.Style["background-color"] = "#aaeeaa";
    p.ID = "childPanel";
    p.ClientIDMode = System.Web.UI.ClientIDMode.Static;
    p.Controls.Add(new LiteralControl("<div id=\"div111\" runat=\"server\">Hello, world!</div>"));
    declaredPanel.Controls.Add(p);
    Panel p2 = declaredPanel.FindControl("childPanel") as Panel;
    string colorCode = p2.Style["background-color"]; // reports "#aaeeaa"

Produces this:

<div id="declaredPanel">
    <div id="childPanel" style="background-color:#aaeeaa;">
        <div id="div111" runat="server">Hello, world!</div>
    </div>
</div>

But doesn't adding runat="server" make it a server control? Can I just access the control directly? — Elad Lachmi, Jun 01 '11 at 07:44
+1. Also div is not a control, and it is not posted to server. — Adeel, Jun 01 '11 at 07:44

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

You have to add dynamic controls in OnInit event and event at postback. If not - all controls will be not visible at postback HOW TO: Dynamically Create Controls in ASP.NET by Using Visual C# .NET

Note When you create dynamic controls on a Web Form, the controls must be created and added to the controls collection either in the OnInit or in the Page_Load events. Otherwise, the controls behave unexpectedly.

score 0 · Answer 3 · edited May 23 '17 at 11:48

Use a Panel instead of a LiteralControl. It'll be rendered as a DIV and will be found by FindControl via it's ID. You can't find the div because it is "wrapped" inside the LiteralControl. Control.FindControl searches the current NamingContainer for a control(runat=server) with the given ID. Remember that FindControl won't find elements recursively(f.e. in all TableCells on a page).

Have a look here for a ... Better way to find control in ASP.NET

score 0 · Answer 4 · answered Jun 01 '11 at 07:45

Try the following:

LiteralControl literalControl = new LiteralControl();
literalControl.ID = "divLiteralControl";
literalControl.Text = ...
subCell.Controls.Add(literalControl);

Then use the FindControl method to get the literal control and edit its text.

LiteralControl literalControl = 
    (LiteralControl) subCell.FindControl("divLiteralControl");
literalControl.Text = ...

Page.FindControl comes back null for DIV

4 Answers4